Guidelines For Successful Use Of The Rolling Shutter; Flash Exposure For Fast Moving Objects - Basler A400K User Manual

3.4.1 Guidelines for Successful Use of the Rolling Shutter

To successfully use the rolling shutter functionality of the camera, make sure that you observe the
guidelines listed below.
• Exposure time can only be set incrementally in multiples of 4.56 µs. Formula:
where N must be an integer and > 0. Exposure time can range from 4.56 µs to 19.12 s.
• The runtime of the sensor reset and readout depends on the height of the area of interest
(AOI, see page 3-24). The formula below can be used to calculate the runtime:
• The formula below can be used to calculate the total time it takes to reset, expose and read
out a single frame:
Examples:
(A) The height of the area of interest (AOI) is 1726 lines (full resolution):
Total runtime = 4.56 µs x (1726 - 1) + Exposure time = 7866 µs + Exposure time
(B) The height of the area of interest (AOI) is only 200 lines:
Total runtime = 4.56 µs x (200 - 1) + Exposure time = 907.4 µs + Exposure time
• Imaging of fast moving objects requires a flash exposure within the camera's flash window
(see Section 3.4.2).

3.4.2 Flash Exposure for Fast Moving Objects

Imaging of fast moving objects requires a flash exposure. If flash exposure is not used, image
distortions will occur due to the exposure's 4.56 µs offset from one line to the next.
Due to the exposure's 4.56 µs offset from one line to the next, there is a limited time interval where
all pixel lines are open, that is, all pixels are exposed to light simultaneously. This time interval is
called the "flash window" of the camera (see
The flash window opens when exposure is started in the last pixel line within the area of interest
(AOI) and it closes when readout is started in the first pixel line within the AOI. The width of the
flash window is calculated using the below formula:
A400k cameras output a flash trigger signal that can be used to trigger flash exposure. The flash
trigger signal can be programmed to be high as long as the flash window is open, that is, all pixel
lines are exposed to light and the flash should occur (see Section
Basler A400k
Exposure time
Reset runtime = Readout runtime = 4.56 µs x (AOI Height - 1)
Total frame exposure runtime
Flash window width [µs] = Exposure time [µs] - (AOI Height x 4.56 µs)
DRAFT
× 4.56 μs
N
=
4.56 μs × (
=
Figure 3-9).
Basic Operation and Features
)
AOI Height 1 + Exposure time
–
2.5.8 on page 2-32).
3-9